Method and structure for forming silicon germanium FinFET

ABSTRACT

A method of a forming a plurality of semiconductor fin structures that includes forming a sacrificial gate structure on a hardmask overlying a channel region portion of the plurality of sacrificial fins of a first semiconductor material and forming source and drain regions on opposing sides of the channel region. The sacrificial gate structure and the sacrificial fin structure are removed. A second semiconductor material is formed in an opening provided by removing the sacrificial gate structure and the sacrificial fin structure. The second semiconductor material is etched selective to the hardmask to provide a plurality of second semiconductor material fin structures. A function gate structure is formed on the channel region.

BACKGROUND Technical Field

The present invention relates to semiconductor devices, and moreparticularly to semiconductor devices including fin structures.

Description of the Related Art

With the continuing trend towards miniaturization of integrated circuits(ICs), there is a need for transistors to have higher drive currentswith increasingly smaller dimensions. The use of non-planarsemiconductor devices such as, for example, silicon fin field effecttransistors (FinFETs) may be the next step in the evolution ofcomplementary metal oxide semiconductor (CMOS) devices.

SUMMARY

In one embodiment, a method of a forming a plurality of semiconductorfin structures is described that includes forming a sacrificial gatestructure on a hardmask overlying a channel region portion of aplurality of sacrificial fins of a first semiconductor material, inwhich isolation regions are present at the base of the plurality ofsacrificial fins. The method may continue with forming source and drainregions on opposing sides of the channel region portion of the pluralityof sacrificial fins; and removing the sacrificial gate structure and thesacrificial fin structure selectively to the hardmask. A secondsemiconductor material is formed in an opening provided by removing thesacrificial gate structure and the sacrificial fin structure. The secondsemiconductor material is etched selectively to the hardmask to providea plurality of second semiconductor material fin structures. Afunctional gate structure is formed on a channel region portion of theplurality of second semiconductor material fin structures.

In another embodiment, a method of a forming a plurality ofsemiconductor fin structures is described that includes forming asacrificial gate structure on a hardmask overlying a channel regionportion of a plurality of sacrificial fins of a first semiconductormaterial, in which isolation regions are present at the base of theplurality of sacrificial fins. The method may continue with formingsource and drain regions on opposing sides of the channel region portionof the plurality of sacrificial fins; and removing the sacrificial gatestructure and the sacrificial fin structure selectively to the hardmask.A second semiconductor material is formed in an opening provided byremoving the sacrificial gate structure and the sacrificial finstructure. The second semiconductor material is etched selectively tothe hardmask to provide a plurality of second semiconductor material finstructures. A functional gate structure is formed on a channel regionportion of the plurality of second semiconductor material finstructures.

In another embodiment, a semiconductor device is provided including asilicon and germanium containing fin structure epitaxially present atopa silicon substrate, wherein a base of the silicon germanium finstructure includes lateral extensions. A gate structure is present on achannel portion of the silicon and germanium containing fin structure.In one embodiment, source and drain regions are present on opposingsides of the channel portion of the silicon and germanium containing finstructure. The lateral extensions of the silicon and germaniumcontaining fin structure undercut an edge of the source and drainregions.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1A is a top down view depicting one embodiment of forming finstructures from a first semiconductor material using a hardmask and anetch method, wherein isolation regions are formed between adjacent finstructures.

FIG. 1B is a side cross-sectional view along section line A-A′ in FIG.1A illustrating a cross section along a length of a fin structure.

FIG. 1C is a side cross-sectional view along section line B-B′ in FIG.1A illustrate a cross section across the length of a plurality of finstructures.

FIG. 2A is a top down view depicting one embodiment of forming asacrificial gate structure on the channel region of the fin structuresdepicted in FIG. 1A, and forming source and drain regions on opposingsides of the channel region.

FIG. 2B is a side cross-sectional view along section line A-A′ in FIG.2A.

FIG. 2C is a side cross-sectional view along section line B-B′ in FIG.2A.

FIG. 3A is a top down view depicting one embodiment removing thesacrificial gate structure from the device structure depicted in FIG.2A.

FIG. 3B is a side cross-sectional view along section line A-A′ in FIG.3A.

FIG. 4A is a top down view depicting isotropically etching the finstructures of the first semiconductor material.

FIG. 4B is a side cross-sectional view along section line A-A′ in FIG.4A.

FIG. 4C is a side cross-sectional view along section line B-B′ in FIG.4A.

FIG. 5A is a top down view depicting epitaxially growing a secondsemiconductor material in the opening provided by removing thesacrificial gate structure and the sacrificial fin structure.

FIG. 5B is a side cross-sectional view along section line A-A′ in FIG.5A.

FIG. 5C is a side cross-sectional view along section line B-B′ in FIG.5A.

FIG. 6A is a top down view depicting etching the second semiconductormaterial selectively to the hardmask to provide a plurality of secondsemiconductor material fin structures.

FIG. 6B is a side cross-sectional view along section line A-A′ in FIG.6A.

FIG. 6C is a side cross-sectional view along section line B-B′ in FIG.6A.

FIG. 7A is a top down view of forming gate sidewall spacer and forming anotch region underlying a portion of the gate sidewall spacers.

FIG. 7B is a side cross-sectional view along section line A-A′ in FIG.7A.

FIG. 7C is a side cross-sectional view along section line B-B′ in FIG.7A.

FIG. 8A is a top down view of forming a function gate structure for aFinFET device on the structure depicted in FIG. 7A.

FIG. 8B is a side cross-sectional view along section line A-A′ in FIG.8A.

FIG. 8C is a side cross-sectional view along section line B-B′ in FIG.8A.

FIG. 9A is a top down view of an initial structure used for formingFinFET in accordance with a second embodiment of the present invention,in which the initial structure includes a sacrificial gate structurethat is present on a channel region of fin structures of a firstsemiconductor material, wherein source and drain regions are on opposingsides of the channel region.

FIG. 9B is a side cross-sectional view along section line A-A′ in FIG.9A illustrating a cross section along a length of a fin structure.

FIG. 9C is a side cross-sectional view along section line B-B′ in FIG.9A illustrate a cross section across the length of a plurality of finstructures.

FIG. 10A is a top down view depicting one embodiment removing thesacrificial gate structure from the device structure depicted in FIG.9A.

FIG. 10B is a side cross-sectional view along section line A-A′ in FIG.10A.

FIG. 10C is a side cross-sectional view along section line B-B′ in FIG.10A.

FIG. 11A is a top down view depicting isotropically etching the finstructures of the first semiconductor material that are depicted in FIG.10A.

FIG. 11B is a side cross-sectional view along section line A-A′ in FIG.11A.

FIG. 11C is a side cross-sectional view along section line B-B′ in FIG.11A.

FIG. 12A is a top down view depicting epitaxially growing a secondsemiconductor material in the opening provided by removing thesacrificial gate structure and the sacrificial fin structure, andetching the second semiconductor material selectively to the hardmask toprovide a plurality of second semiconductor material fin structures.

FIG. 12B is a side cross-sectional view along section line A-A′ in FIG.12A.

FIG. 12C is a side cross-sectional view along section line B-B′ in FIG.12A.

FIG. 13A is a top down view depicting forming isolation regions betweenadjacent second semiconductor material fin structures.

FIG. 13B is a side cross-sectional view along section line A-A′ in FIG.13A.

FIG. 13C is a side cross-sectional view along section line B-B′ in FIG.13A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Detailed embodiments of the claimed methods, structures and computerproducts are disclosed herein; however, it is to be understood that thedisclosed embodiments are merely illustrative of the claimed structuresand methods that may be embodied in various forms. In addition, each ofthe examples given in connection with the various embodiments isintended to be illustrative, and not restrictive. Further, the figuresare not necessarily to scale, some features may be exaggerated to showdetails of particular components. Therefore, specific structural andfunctional details disclosed herein are not to be interpreted aslimiting, but merely as a representative basis for teaching one skilledin the art to variously employ the methods and structures of the presentdisclosure.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment. For purposes of thedescription hereinafter, the terms “upper”, “over”, “overlying”,“lower”, “under”, “underlying”, “right”, “left”, “vertical”,“horizontal”, “top”, “bottom”, and derivatives thereof shall relate tothe embodiments of the disclosure, as it is oriented in the drawingfigures. The term “positioned on” means that a first element, such as afirst structure, is present on a second element, such as a secondstructure, wherein intervening elements, such as an interface structure,e.g. interface layer, may be present between the first element and thesecond element. The term “direct contact” means that a first element,such as a first structure, and a second element, such as a secondstructure, are connected without any intermediary conducting, insulatingor semiconductor layers at the interface of the two elements.

As used herein, the term “fin structure” refers to a semiconductormaterial, which can be employed as the body of a semiconductor device,in which the gate structure is positioned around the fin structure suchthat charge flows down the channel on the two sidewalls of the finstructure and optionally along the top surface of the fin structure. Thefin structures disclosed herein may provide the active region, i.e., thesource, drain and channel portions, of fin structures for Fin FieldEffect Transistors (FinFET). A field effect transistor (FET) is asemiconductor device in which output current, i.e., source-draincurrent, is controlled by the voltage applied to a gate structure to thesemiconductor device. A field effect transistor has three terminals,i.e., gate structure, source region and drain region. A finFET is asemiconductor device that positions the channel region of thesemiconductor device in a fin structure. As used herein, the term“drain” means a doped region in semiconductor device located at the endof the channel region, in which carriers are flowing out of thetransistor through the drain. The term “source” is a doped region in thesemiconductor device, in which majority carriers are flowing into thechannel region.

The structures and methods that are disclosed herein provide a methodfor providing a silicon germanium (SiGe) fin structure, such as asilicon germanium (SiGe) fin structure for use as a channel region inp-type field effect transistors (pFETs). Further, in electrical devicesincluding multiple semiconductor devices, such as different conductivitytypes, i.e., n-type or p-type, FinFETs, isolation regions may beemployed to provide for device isolation between the differentconductivity type devices. The isolation regions, such as shallow trenchisolation (STI) regions, may be formed on a substrate including theaforementioned fin structures. Stability of the shallow trench isolationregion (STI) region can be advantageous for the device performance.Stability of the shallow trench isolation (STI) regions can be increasedwith high temperature annealing. If a silicon germanium (SiGe) finstructure, such as a silicon germanium (SiGe) fin structure for aMOSFET, is formed before the shallow trench isolation (STI) region, thethermal budget of the annealing to increase the quality of the STI canresult in potential SiGe strain relaxation and defect formation.

The methods and structures described herein form channel regions ofsilicon germanium (SiGe), such as silicon germanium (SiGe) finstructures, late in the process flow to prevent from the thermal budgetof the STI annealing process, which occurs early in the process flow,impacting the quality of the silicon germanium (SiGe). For example, insome embodiments, the methods provided herein form SiGe Fin structuresafter shallow trench isolation (STI) region formation to avoid defectsand strain relaxation in the SiGe channel. In some embodiments, themethods provided herein form SiGe Fin structures after shallow trenchisolation (STI) region formation and after source/drain junctionformation, which is another high thermal budget process, to avoiddefects and strain relaxation in the SiGe channel. The methods andstructures of the present disclosure are now discussed with more detailreferring to FIGS. 1A-8C.

In some embodiments, the method of forming the semiconductor deviceincluding the silicon germanium (SiGe) fin structures can begin withforming a sacrificial gate structure 25 on a hardmask 15 overlying achannel region portion of a plurality of sacrificial fin structures 10of a first semiconductor material, as depicted in FIGS. 1A-2C. Isolationregions 20 are present at the base of the plurality of sacrificial finstructures 10.

FIGS. 1A-1C depict one embodiment of forming sacrificial fin structures10 from a first semiconductor material using a hardmask 15 and an etchmethod, wherein isolation regions 20 are formed between adjacentsacrificial fin structures 10. In some embodiments, the plurality ofsacrificial fin structures 10 may be composed of a type IVsemiconductor, such as silicon (Si). In some embodiments, the pluralityof sacrificial fin structures 10 may be formed from a bulk semiconductorsubstrate. The bulk semiconductor substrate, and subsequently the finstructures 5 that are formed therefrom, can be composed of a type IVsemiconductor material. For example, the semiconductor material of thesubstrate 1, (as well as the sacrificial fin structures 10) may include,but is not limited to silicon, strained silicon, a silicon carbon alloy(e.g., silicon doped with carbon (Si:C), silicon germanium, a silicongermanium and carbon alloy (e.g., silicon germanium doped with carbon(SiGe:C), silicon alloys, germanium, germanium alloys, and combinationsthereof. In some other embodiments, the substrate may be composed ofanother semiconductor material besides a type IV semiconductor, such asa type III-V semiconductor material, such as gallium arsenic, indiumarsenic, indium phosphide, as well as other III/V and II/VI compoundsemiconductors.

The plurality of sacrificial fin structures 10 may be formed depositionphotolithography and etch processes. Alternatively, the sacrificial finstructures 10 can be formed by any other suitable patterning techniqueincluding but not limited to sidewall image transfer (SIT), self-aligneddouble patterning (SADP), self-aligned quadruple patterning (SAQP),self-aligned multiple patterning (SAMP). For example, forming theplurality of sacrificial fin structures 10 may include forming adielectric layer (for forming a hardmask 15) on an upper surface of thesubstrate; etching the dielectric layer to form a hardmask 15; and thenetching the substrate using the hardmask 15 with an anisotropic etch toa first depth to provide the sacrificial fin structures 10.

The dielectric layer that provides the hardmask 15 may be composed ofany dielectric layer or multiple layers that can function as an etchmask for etching the first semiconductor material, e.g., bulksemiconductor substrate, for forming the sacrificial fin structures 10.In some embodiments, the dielectric layer that provides the hardmask 15may be composed of an oxide, nitride or oxynitride material. Forexample, when the sacrificial fin structures 10 being patterned arecomposed of silicon (Si), the dielectric layer that provides thehardmask 15 may be composed of silicon nitride, or a combination ofmultiple materials such as silicon nitride on top of a silicon oxide.The dielectric layer may be deposited using chemical vapor deposition(CVD), e.g., plasma enhanced chemical vapor deposition (PECVD). Othersuitable deposition techniques include atomic layer deposition (ALD),physical vapor deposition (PVD).

The dielectric layer may be patterned using photolithography and etchedto provide the geometry for the hard mask 15. More specifically, aphotoresist etch mask may be formed overlying the portion of thedielectric layer that provides the hardmask 15, and then the exposedportions of the dielectric layer may be removed using an etch process,such as reactive ion etching (RIE). Alternatively, the sacrificial finstructures 10 can be formed by any other suitable patterning techniqueincluding but not limited to sidewall image transfer (SIT), self-aligneddouble patterning (SADP), self-aligned quadruple patterning (SAQP),self-aligned multiple patterning (SAMP).

In a following process step, the hard mask 15 protects the portions ofthe substrate, i.e., first semiconductor material, that provides the finstructures 10, while the exposed portions of the substrate that are notcovered by the hard mask 15 are etched to form the trenches thatseparate the sacrificial fin structures 10. Similar to the etch processfor patterning the hard mask 15, the etch process for forming theplurality of fin structures 10 may be an anisotropic etch, such asreactive ion etch (RIE), plasma etch, laser etching or a combinationsthereof. The etch process removes the exposed portions of the substrate,i.e., first semiconductor material, selectively to the hard mask 15. Asused herein, the term “selective” in reference to a material removalprocess denotes that the rate of material removal for a first materialis greater than the rate of removal for at least another material of thestructure to which the material removal process is being applied. Forexample, in one embodiment, a selective etch may include an etchchemistry that removes a first material selectively to a second materialby a ratio of 10:1 or greater, e.g., 100:1 or greater, or 1000:1 orgreater.

The sacrificial fin structures 10 formed at this stage of the processflow may have a first height ranging from 5 nm to 200 nm. In anotherembodiment, each of the fin structures 10 has a first height rangingfrom 10 nm to 100 nm. In one example, each of the sacrificial finstructures 10 has a height ranging from 20 nm to 50 nm. Each of theplurality of sacrificial fin structures 10 may have a width ranging from5 nm to 20 nm. In another embodiment, each of the sacrificial finstructures 10 has a width ranging from 5 nm to 15 nm. In one example,each sacrificial fin structures 10 has a width that is equal to 10 nm.The pitch separating adjacent sacrificial fin structures 10 may rangefrom 10 nm to 50 nm. In another embodiment, the pitch 1 separatingadjacent sacrificial fin structures may range from 20 nm to 45 nm. Inone example, the pitch is equal to 30 nm. Although three sacrificial finstructures are depicted in FIG. 1A, the present disclosure is notlimited to only this example. It is noted that any number of finstructures 10 may be formed from the semiconductor substrate.

Still referring to FIGS. 1A-1C, isolation regions, i.e., shallow trenchisolation (STI) regions 20 may be formed between adjacent sacrificialfin structures 10 at the base of the sacrificial fin structures 10. Forexample, isolation regions may be formed by depositing a dielectric inthe trench that is separating the adjacent sacrificial fin structures10. The dielectric material for the isolation regions may be an oxide,such as silicon oxide. Other dielectric materials for the isolationregions may include nitride, such as silicon nitride, and/or siliconoxynitride materials, e.g., silicon oxynitride. The isolation regionsmay be formed using a chemical vapor deposition (CVD) process, such asplasma enhanced chemical vapor deposition (PECVD), metal organicchemical vapor deposition (MOCVD) and/or high density plasma chemicalvapor deposition (HDPCVD). The height of the dielectric material for theshallow trench isolation (STI) regions 20 may be set using an etchprocess, such as reactive ion etching (RIE).

The dielectric material of the isolation region, e.g., shallow trenchisolation (STI) region 20, may be densified to increase the quality ofthe isolation region using a high temperature anneal. For example, theanneal process may include an anneal temperature ranging from 400° C. to1200° C. In some other examples, the anneal process may include ananneal temperature of approximately 900° C.

FIGS. 2A-2C depict one embodiment of forming a sacrificial gatestructure 25 on the hardmask 15 that is present on the channel region ofthe sacrificial fin structures 10 depicted in FIG. 1A, and formingsource and drain regions 30, 35 on opposing sides of the channel region.

FIGS. 2A-2C depicting forming a sacrificial gate structures 25 on thehardmask 15 that is present on an upper surface of the plurality ofsacrificial fin structures 10. The term “sacrificial” as used todescribe the sacrificial gate conductor 25 denotes that the structure ispresent during the process sequence, but is not present in the finaldevice structure, in which the sacrificial structure provides an openingthat dictates the size and geometry of a later formed functional gatestructure. The sacrificial material that provides the replacement gatestructure 25 may be composed of any material that can be etchedselectively to the underlying hardmask 15 that is atop the sacrificialfin structure 10. In one embodiment, the sacrificial material thatprovides the sacrificial gate structure 25 may be composed of adielectric, such as an oxide, nitride or oxynitride. The sacrificialgate structure 25 may also be composed of a semiconductor material, suchas polysilicon.

The sacrificial material may be patterned and etched to provide thesacrificial gate structure 25. Specifically, and in one example, apattern is produced by applying a photoresist to the surface to beetched, exposing the photoresist to a pattern of radiation, and thendeveloping the pattern into the photoresist utilizing a resistdeveloper. Once the patterning of the photoresist is completed, thesections of the sacrificial material covered by the photoresist areprotected to provide the sacrificial gate structure 25, while theexposed regions are removed using a selective etching process thatremoves the unprotected regions. Following formation of sacrificial gatestructure 25, the photoresist may be removed. A dielectric spacer 26 maybe present on a sidewall of the sacrificial gate structure 25. Stillreferring to FIGS. 2A-2C, source and drain regions 30, 35 may be formedon opposing sides of the channel region of the sacrificial fin structure10. The source and drain regions 30, 35 may be composed of epitaxiallyformed and in situ doped semiconductor material.

The term “epitaxial semiconductor material” denotes a semiconductormaterial that has been formed using an epitaxial deposition or growthprocess. “Epitaxial growth and/or deposition” means the growth of asemiconductor material on a deposition surface of a semiconductormaterial, in which the semiconductor material being grown hassubstantially the same crystalline characteristics as the semiconductormaterial of the deposition surface. In some embodiments, when thechemical reactants are controlled and the system parameters setcorrectly, the depositing atoms arrive at the deposition surface withsufficient energy to move around on the surface and orient themselves tothe crystal arrangement of the atoms of the deposition surface. Thus, insome examples, an epitaxial film deposited on a {100} crystal surfacewill take on a {100} orientation.

In some embodiments, the epitaxial semiconductor material that providesthe source and drain regions 30, 35 may be composed of silicon (Si),germanium (Ge), silicon germanium (SiGe), silicon doped with carbon(Si:C) or the epitaxial semiconductor material may be composed of a typeIII-V compound semiconductor, such as gallium arsenide (GaAs). Theepitaxial semiconductor material may be in situ doped to a p-type orn-type conductivity. The term “in situ” denotes that a dopant, e.g.,n-type or p-type dopant, is introduced to the base semiconductormaterial, e.g., silicon or silicon germanium, during the formation ofthe base material. For example, an in situ doped epitaxial semiconductormaterial may introduce n-type or p-type dopants to the material beingformed during the epitaxial deposition process that includes n-type orp-type source gasses.

In the embodiments in which the finFET device being formed has n-typesource and drain regions 30, 35, and is referred to as an n-type finFET,the doped epitaxial semiconductor material is doped with an n-typedopant to have an n-type conductivity. In the embodiments in which thefinFET device being formed has p-type source and drain regions 30, 35,and is referred to as a p-type finFET, the doped epitaxial semiconductormaterial is doped with a p-type dopant to have a p-type conductivity. Asused herein, “p-type” refers to the addition of impurities to anintrinsic semiconductor that creates deficiencies of valence electrons.In a type IV semiconductor, such as silicon, examples of p-type dopants,i.e., impurities, include but are not limited to, boron, aluminum,gallium and indium. As used herein, “n-type” refers to the addition ofimpurities that contributes free electrons to an intrinsicsemiconductor. In a type IV semiconductor, such as silicon, examples ofn-type dopants, i.e., impurities, include but are not limited toantimony, arsenic and phosphorous.

FIGS. 3A-3C depict one embodiment removing the sacrificial gatestructure 25. In some embodiments, prior to removing the sacrificialgate structure 25, a dielectric layer 40 is deposited on at least thesource and drain regions 30, 35, wherein the upper surface of thedielectric layer 40 is coplanar with the upper surface of thesacrificial gate structure 25. The dielectric layer 40 may be anynon-crystalline material. For example, the dielectric 40 may be carbonbased, such as amorphous carbon (α-C), or an oxide, such as poroussilicon dioxide. It is noted that the above examples of the materialcompositions for the dielectric layer 40 have been provided forillustrative purposes only, and are not intended to limit the presentdisclosure.

The dielectric layer 40 may be formed by deposition, such as chemicalvapor deposition, e.g., plasma enhanced chemical vapor deposition, orcan be formed using a growth process, such as thermal oxidation. In someother embodiments, the dielectric layer 40 may be deposited using spinon deposition methods. In other embodiments, the dielectric layer 40 maybe deposited using spin on deposition. To provide that the upper surfaceof the dielectric layer 40 is coplanar with the upper surface of thesacrificial gate structure 25, the deposited dielectric layer 40 isplanarized using chemical mechanical planarization (CMP).

FIGS. 3A-3B depict removing the sacrificial gate structure 25 to providean opening 21 through the dielectric layer 40 to the hardmask 15 that ispresent on the sacrificial fin structure 10. In some embodiments, theetch process for removing the sacrificial gate structure 25 to providethe opening 21 to the replacement fin structure 10 may be a selectiveetch process. For example, the etch process for forming the opening 21may remove the material of the sacrificial gate structure 25 selectivelyto the dielectric material 40 and the dielectric spacer 26. In someembodiments, the etch process for recessing the exposed portion of thesacrificial gate structure 25 may also be selective to the sacrificialfin structure 10. As used herein, an “anisotropic etch process” denotesa material removal process in which the etch rate in the directionnormal to the surface to be etched is greater than in the directionparallel to the surface to be etched. One anisotropic etch that can beused during this stage of the present process flow may be reactive ionetching (RIE). Other examples of anisotropic etching that can be used atthis point of the present invention include ion beam etching, plasmaetching or laser ablation. In other embodiments, the etch process forremoving the sacrificial gate structure 25 may be an isotropic etch,such as a wet chemical etch. Or a combination of both isotropic andanisotropic etch processes.

FIGS. 4A-4C depict removing the sacrificial fin structure 10 selectivelyto the dielectric layer 40 and the hardmask 15 to provide a fin opening21′. In some embodiments, the etch process for removing the replacementfin structure 10 is an isotropic etch. By isotropic it is meant that theetch process is non-directional.

In some embodiments, the etch process for removing the sacrificial finstructure 10 and forming the fin opening 21′ includes a lateral etchingcomponent in addition to a vertical, i.e., recessing, etching component.The isotropic etch can remove the entirety of the sacrificial finstructures 10, as well as a portion of the supporting portion of thesemiconductor substrate 5. In some embodiments, by removing a portion ofthe semiconductor substrate 5 that is underlying the sacrificial finstructures 10, the isotropic etch produces a trench in the semiconductorsubstrate 5, which includes a notch portion 22 that is presentundercutting the source and drain regions 30, 35.

The isotropic etch for removing the sacrificial fin structures 10 andforming the fin opening 21′ may be a wet chemical etch. In otherembodiments, the isotropic etch for removing the sacrificial finstructures 10 and forming the fin opening 21′ may be a gas plasma etch.In some embodiments, the isotropic etch for forming the fin opening 25may remove the semiconductor material, e.g., silicon, of the sacrificialfin structures 10 and the semiconductor substrate 5 selectively to thedielectric 20. The isotropic etch used at this stage of the process flowmay also be selective to the remaining portion of the sacrificial gatestructures 25.

FIGS. 5A-5D depict epitaxially growing functional fin structures 45 of asecond semiconductor material on a growth surface provided by thesemiconductor substrate 5 at the base of the fin opening 21′. The secondsemiconductor material that is being epitaxially grown substantiallyfills the gate opening 21, the fin opening 21′, and the notch 22. Thesecond semiconductor material may also encapsulate the hardmask 15. Theepitaxial material, i.e., second semiconductor material, for thefunction fin structures 45 may be composed of a silicon and germaniumcontaining semiconductor. For example, the second semiconductor materialthat is epitaxially grown for the functional fin structures 45 may becomposed of silicon germanium (SiGe). In some embodiments, in which thesecond semiconductor material that is epitaxially grown for thefunctional fin structures 45 are composed of silicon germanium, thesilicon sources for epitaxial deposition may be selected from the groupconsisting of silane, disilane, trisilane, tetrasilane,hexachlorodisilane, tetrachlorosilane, dichlorosilane, trichlorosilane,methylsilane, dimethylsilane, ethylsilane, methyldisilane,dimethyldisilane, hexamethyldisilane and combinations thereof, and thegermanium gas sources may be selected from the group consisting ofgermane, digermane, halogermane, dichlorogermane, trichlorogermane,tetrachlorogermane and combinations thereof.

It is noted that the epitaxial deposition process that forms the secondsemiconductor material 45 fills the notch portion 22 of the opening. Insome embodiments, this provides lateral extensions 46 of the silicon andgermanium containing fin structure that undercut an edge of the sourceand drain regions 30, 35. The lateral extensions 46 may undercut theedge of the source and drain regions 30, 35 by a dimension ranging from1 nm to 15 nm. In some embodiments, the lateral extensions 46 mayundercut the edge of the source and drain regions 30, 35 by a dimensionranging from 1 nm to 10 nm. In yet another embodiment, the lateralextensions 46 may undercut the edge of the source and drain regions 30,35 by a dimension ranging from 2 nm to 5 nm. In some embodiments, theepitaxy can overgrow above the top surface of ILD 40. A planarizationprocess such as chemical mechanical polish (CMP) can be used to removethe epitaxy material above the ILD.

FIGS. 6A-6C depicting etching the second semiconductor material 45selectively to the hardmask 15 to provide a plurality of secondsemiconductor material fin structures, i.e., for providing thefunctional fin structures 45. The etch process used at this stage of theprocess flow may be an anisotropic etch. The hardmask 15 provides theetch mask for dictating the geometry of the plurality of secondsemiconductor material fin structures, i.e., the functional finstructures 45. Therefore, because the hardmask 15 also dictated thegeometry of the sacrificial fin structures 10, as described above withreference to FIGS. 1A-1C, the second semiconductor material finstructures, i.e., the functional fin structures 45, will havedimensions, i.e., height, width and pitch, that are the same as thesedimensions for the sacrificial fin structures 10, which are providedabove in the description of FIGS. 1A-1C.

One anisotropic etch that can be used during this stage of the presentprocess flow may be reactive ion etching (RIE). Reactive Ion Etching(RIE) is a form of plasma etching in which during etching the surface tobe etched is placed on the RF powered electrode. Moreover, during RIEthe surface to be etched takes on a potential that accelerates theetching species extracted from plasma toward the surface, in which thechemical etching reaction is taking place in the direction normal to thesurface. Other examples of anisotropic etching that can be used at thispoint of the present invention include ion beam etching, plasma etchingor laser ablation.

It is noted that the lateral extensions 46 remain in the devicestructure following this etch step.

FIGS. 7A-7C depict forming gate sidewall spacers 55 and forming anundercut region 56 underlying a portion of the gate sidewall spacers 55.The process flow for forming the gate sidewall spacers 55 includesthinning the hardmask 15, forming a low-k gate sidewall spacer 55 onsidewalls of a gate opening atop a remaining portion of the hardmask15′, isotropically etching the remaining portion of the hardmask 15′ toform the undercut region 56 underlying the low-k gate sidewall spacer55.

Thinning the hardmask 15 may be accomplished with an etch process.

The low-k gate sidewall spacers 55 are formed using deposition and etchprocesses. A low-k dielectric material has a dielectric constant that isless than 7.0, e.g., less than 5.0. In one embodiment, the low-kmaterial that provides the outer spacer layer 25 may have a dielectricconstant ranging from 1.0 to 3.5. In another embodiment, the low-kmaterial that provides the outer spacer layer 25 may have a dielectricconstant ranging from 1.75 to 3.2. Some examples of materials that aresuitable for the gate sidewall spacer 55 may include silicon boroncarbon nitride (SiBCN), silicon oxycarbonitride (SiOCN), siliconcarbonitride (SiCN), silicon oxycarbide (SiOC), silicon oxynitride(SiON), and/or silicon oxide Other low-k materials that may also be usedfor the low-k gate sidewall spacer 55 may include fluorine doped silicondioxide, carbon doped silicon dioxide, porous silicon dioxide, porouscarbon doped silicon dioxide, organosilicate glass (OSG), diamond-likecarbon (DLC) and combinations thereof.

In some embodiments, the low-k dielectric layer material for the low-kgate sidewall spacer may be conformally deposited on the sidewalls ofthe gate structure opening using atomic layer deposition (ALD), orchemical vapor deposition (CVD). Variations of CVD processes suitablefor forming the first dielectric layer include, but are not limited to,Atmospheric Pressure CVD (APCVD), Low Pressure CVD (LPCVD) and PlasmaEnhanced CVD (PECVD), Metal-Organic CVD (MOCVD) and combinations thereofmay also be employed.

Following deposition, an etch process removes the horizontallyorientated portions of the low-k dielectric material layer, wherein theremaining portions that are vertically orientated provide the low-k gatesidewall spacers 55. The etch process used at this stage of the processflow is an anisotropic etch, such as reactive ion etching.

A central portion of the thinned hardmask 15′ that is not covered by thelow-k gate sidewall spacers 55 remains exposed. The central portion ofthe thinned hardmask 15′ is then etched with an isotropic etch to exposea channel region surface of the second semiconductor material finstructures, i.e., the functional fin structures 45. The isotropic etchmay be provided by a wet chemical etch and/or a gas/plasma etch. Theetch process for removing the exposed portion of the thinned hardmask15′ may be selective to the low-k gate sidewall spacers 55, as well asthe second semiconductor material fin structures, i.e., the functionalfin structures 45.

The isotropic etch process for removing the central portion of thethinned hardmask 15′ also laterally etches the thinned hardmask 15′removing a portion that is underlying the low-k gate sidewall spacers55. This provides an undercut region 56 underlying the low-k gatesidewall spacer 55. The undercut region 56 may undercut the interioredge of the low-k gate sidewall spacer 55 by a dimension ranging from 1nm to 10 nm. In some embodiments, the undercut region 56 may undercutthe interior edge of the low-k gate sidewall spacer 55 by a dimensionranging from 1 nm to 5 nm.

FIGS. 8A-8C depicting forming a function gate structure 50 for a FinFETdevice in the gate opening 21. The functional gate structure 50 includesa gate dielectric 51 and a gate conductor 52. The “functional gatestructure” functions to switch the semiconductor device from an “on” to“off” state, and vice versa. The functional gates structure 50 is formedon the channel region of the active region portion of the finstructures, i.e., functional fin structures 45 of a second semiconductormaterial. The gate structure 50 typically includes at least a gatedielectric 51 that is present on the channel region of the fin structure45 and a gate electrode 52 that is present on the gate dielectric 51.

In one embodiment, the at least one gate dielectric layer 51 includes,but is not limited to, an oxide, nitride, oxynitride and/or silicatesincluding metal silicates, aluminates, titanates and nitrides. In someembodiments, the gate dielectric 51 may be composed of a high-k gatedielectric. The term “high-k”, as used herein, denotes a dielectricconstant that is greater than the dielectric constant of silicon oxide,which is typically equal to 3.9 (i.e., typically a silicon oxide)measured in vacuum at room temperature (20° C. to 25° C.). Some examplesof high-k dielectric materials suitable for the high-k gate dielectriclayer 51 include hafnium oxide, hafnium silicon oxide, hafnium siliconoxynitride, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide,zirconium silicon oxide, zirconium silicon oxynitride, tantalum oxide,titanium oxide, barium strontium titanium oxide, barium titanium oxide,strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandiumtantalum oxide, lead zinc niobate and combinations thereof. In someembodiments, the high-k dielectric employed for the high-k gatedielectric layer 51 is selected from the group consisting of hafniumoxide (HfO₂), zirconium oxide (ZrO₂), aluminum oxide (Al₂O₃), hafniumsilicate (HfSiO), nitrided hafnium silicate (HfSiON), hafnium oxynitride(HfO_(x)N_(y)), lanthanum oxide (La₃O₂), lanthanum aluminate (LaAlO₃),zirconium silicate (ZrSiO_(x)) and combinations thereof. In oneembodiment, the high-k gate dielectric layer 51 has a thickness thatranges from 1 nm to 10 nm. In another embodiment, the high-k gatedielectric layer 51 has a thickness that ranges from 1 nm to 4 nm. Thethickness of the high-k gate dielectric layer 51 may be conformal.

In some embodiments, in which the gate sidewall spacer 55 has anundercut region 56 (also referred to as notch) present at the baseportion of the spacer, the gate dielectric 51 includes a lateralextension 56 that fills the undercut region 56 in the gate sidewallspacers 55. In some embodiments, the gate dielectric 51 is a conformallayer including a horizontally orientated portion present on the channelregion of the silicon and germanium containing fin structure 45, and avertically orientated portion on interior sidewalls of the gatesidewalls spacers 55, wherein the horizontally orientated portions andthe vertically orientated portions intersect at the portion of the gatedielectric including the lateral extension 56, as depicted in FIGS.8A-8C.

The conductive material of the gate electrode 52 may comprisepolysilicon, SiGe, a silicide, a metal or a metal-silicon-nitride suchas Ta—Si—N. Examples of metals that can be used as the gate electrode 52include, but are not limited to, a metal (e.g., tungsten, titanium,tantalum, ruthenium, zirconium, cobalt, copper, aluminum, lead,platinum, tin, silver, gold), a conducting metallic compound material(e.g., tantalum nitride, titanium nitride, tantalum carbide, titaniumcarbide, titanium aluminum carbide, tungsten silicide, tungsten nitride,ruthenium oxide, cobalt silicide, nickel silicide), carbon nanotube,conductive carbon, graphene, or any suitable combination of thesematerials. The conductive material may further comprise dopants that areincorporated during or after deposition. The layer of conductivematerial for the gate electrode 52 may be doped or undoped. If doped, anin-situ doping deposition process may be employed. Alternatively, adoped conductive material can be formed by deposition, ion implantationand annealing.

The gate electrode 52 may further include a workfunction layer. The workfunction layer may be a nitride, including but not limited to titaniumnitride (TiN), hafnium nitride (HfN), hafnium silicon nitride (HfSiN),tantalum nitride (TaN), tantalum silicon nitride (TaSiN), tungstennitride (WN), molybdenum nitride (MoN), niobium nitride (NbN); acarbide, including but not limited to titanium carbide (TiC) titaniumaluminum carbide (TiAlC), tantalum carbide (TaC), hafnium carbide (HfC),and combinations thereof.

The various layers of the gate structure 50 may be formed by using adeposition method, such as an atomic layer deposition (ALD), a chemicalvapor deposition (CVD) and/or a physical vapor deposition (PVD).

The process flow described with reference to FIGS. 1A-8C provides aFinFET semiconductor device including a silicon and germanium containingfin structure 45 epitaxially present atop a silicon substrate 5, whereina base of the silicon germanium fin structure includes lateralextensions 46. A gate structure 50 present on a channel portion of thesilicon and germanium containing fin structure 45; and source and drainregions 30, 35 are present on opposing sides of the channel portion ofthe silicon and germanium containing fin structure 45, wherein thelateral extensions 46 of the silicon and germanium containing finstructure undercut an edge of the source and drain regions 30, 35.

In some embodiments, the gate structure 50 further includes a gatedielectric 51 present on the channel portion of the silicon andgermanium containing fin structure 45, a gate conductor 52 present onthe gate dielectric 51. In some embodiments, gate sidewall spacers 55are present on the sidewalls of the gate structure 50, wherein the gatesidewall spacers have a notch, i.e., undercut region 56, present at abase portion, and wherein said gate dielectric 51 includes a lateralextension 53 that fills the notch, i.e., undercut region 56, in the gatesidewall spacers. In some embodiments, the gate sidewall spacerscomprise a two layer dielectric stack 15′, 55 including the firstmaterial layer 15′ that is laterally notched to provide said undercutregion 56 that is present underlying a second material layer 55 that ispresent on the first material layer 15′.

The process flow described with reference to FIGS. 1A-8C is only oneprocess flow for the methods of the present invention. The sequence,i.e., order of steps, depicted by the succession of FIGS. 1A-1C to FIGS.8A-8C illustrates only one sequence for the process flow. Otherembodiments have also been contemplated for the process sequence. Forexample, the process sequence for forming a FinFET device including asilicon germanium fin structure 45 may include the steps in an orderedsequence of: 1) forming a sacrificial gate structure 25 on a hardmask 15overlying a channel region portion of the plurality of sacrificial fins10 of a first semiconductor material; 2) forming source and drainregions 30, 35 on opposing sides of the channel region; 3) removing thesacrificial gate structure 25 and the sacrificial fin structure 10selectively to the hardmask 15; 4) forming a second semiconductormaterial 45 in an opening provided by removing the sacrificial gatestructure and the sacrificial fin structure; 5) etching the secondsemiconductor material 45 selectively to the hardmask 15 to provide aplurality of second semiconductor material fin structures 45; 6) formingisolation regions 20 between adjacent second semiconductor material finstructures 45 of said plurality of second semiconductor material finstructures; and 7) forming a functional gate structure 50 on a channelregion portion of the plurality of second semiconductor material finstructures 45. This process flow is now described below with referenceto FIGS. 9A-13C.

FIGS. 9A-9C depicts one embodiment of an initial structure used forforming FinFET, in which the initial structure includes a sacrificialgate structure 25 that is present on a channel region of fin structuresof a first semiconductor material 10, wherein source and drain regions30, 35 are on opposing sides of the channel region. The initialstructure depicted in FIGS. 9A-9C has been described above withreference to FIGS. 1A-3C. The description of the structures and methodsrelating to the structures having reference numbers in FIGS. 1A-3C issuitable for providing the description of the same structures having thesame reference numbers in FIGS. 9A-9C. It is noted that in theembodiment depicted in FIGS. 9A-9C, the isolation regions 20 are notpresent.

FIGS. 10A-10C depicting one embodiment removing the sacrificial gatestructure 25 from the device structure depicted in FIGS. 9A-9C. Thisstep is similar to the step of removing the sacrificial gate structure25 that is described above with reference to FIGS. 3A-3C. Therefore, theabove description of removing the sacrificial gate structure 25 in FIGS.3A-3C is suitable for describing one embodiment of removing thesacrificial gate structure 25 as depicted in FIGS. 10A-10C.

FIGS. 11A-11C depict isotropically etching the fin structures 10, i.e.,removing the fin structures 10, of the first semiconductor material thatare depicted in FIG. 10A. This step is similar to the step of removingthe sacrificial fin structures 10 that are described above withreference to FIGS. 4A-4C. Therefore, the above description of removingthe sacrificial fin structures in FIGS. 4A-4C is suitable for describingone embodiment of removing the sacrificial fin structures 10 as depictedin FIGS. 11A-11C.

FIGS. 12A-12C depicting epitaxially growing a second semiconductormaterial 45, e.g., silicon germanium (SiGe), in the opening provided byremoving the sacrificial gate structure 25 and the sacrificial finstructure 10, and etching the second semiconductor material 45selectively to the hardmask 15 to provide a plurality of secondsemiconductor material fin structures 45. These process steps have beendescribed above with reference to FIGS. 5A-6C. The description of thestructures and methods relating to the structures having referencenumbers in FIGS. 5A-6C is suitable for providing the description of thesame structures having the same reference numbers in FIGS. 12A-12C. Itis noted that isolation regions 20 are not present in FIGS. 12A-12C, aswell as not being present in any of the aforementioned steps.

FIGS. 13A-13C depicting forming isolation regions 20 between adjacentsecond semiconductor material fin structures 45. The isolation regions,i.e., shallow trench isolation (STI) regions 20 may be formed betweenadjacent silicon germanium fin structures 45 at the base of the silicongermanium fin structures 45. For example, isolation regions may beformed by depositing a dielectric in the trench that is separating theadjacent silicon germanium fin structures 45. The dielectric materialfor the isolation regions may be an oxide, such as silicon oxide. Otherdielectric materials for the isolation regions may include nitride, suchas silicon nitride, and/or silicon oxynitride materials, e.g., siliconoxynitride. The isolation regions may be formed using a chemical vapordeposition (CVD) process, such as plasma enhanced chemical vapordeposition (PECVD), metal organic chemical vapor deposition (MOCVD)and/or high density plasma chemical vapor deposition (HDPCVD). Theheight of the dielectric material for the shallow trench isolation (STI)regions 20 may be set using an etch process, such as reactive ionetching (RIE). It is noted that isolation region densification steps,such as high temperature annealing, may be omitted from the process flowdescribed with reference to FIGS. 9A-13C.

In a following process step, a functional gate structure 50 may beformed on a channel region portion of the plurality of secondsemiconductor material fin structures 45 that are depicted in FIGS.13A-13 C. The steps of forming the function gate structure 50, as wellas the gate sidewall spacer 55, have been described above with referenceto FIGS. 7A-8C. The process flow described with reference to FIGS.9A-13C, as well as FIGS. 7A-8C provides a final FinFET device structureincluding a silicon germanium fin structure channel and function gatestructure 50 that is the same as the final FinFET device structure thatis provided by the method described above with reference to FIGS. 1A-8C.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes SixGe1-x where x is less than or equal to 1, etc. In addition,other elements can be included in the compound and still function inaccordance with the present principles. The compounds with additionalelements will be referred to herein as alloys.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS.

Having described preferred embodiments of a methods and structuresdisclosed herein, it is noted that modifications and variations can bemade by persons skilled in the art in light of the above teachings. Itis therefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

What is claimed is:
 1. A method of a forming a plurality ofsemiconductor fin structures comprising: forming a sacrificial gatestructure on a hardmask overlying a channel region portion of aplurality of sacrificial fin structures of a first semiconductormaterial, in which isolation regions are present at the base of theplurality of sacrificial fin structures; forming source and drainregions on opposing sides of the channel region portion of the pluralityof sacrificial fin structures; removing the sacrificial gate structureand the sacrificial fin structures selectively to the hardmask; forminga second semiconductor material in an opening provided by removing thesacrificial gate structure and the sacrificial fin structures; etchingthe second semiconductor material selectively to the hardmask to providea plurality of second semiconductor material fin structures; and forminga functional gate structure on a channel region portion of the pluralityof second semiconductor material fin structures.
 2. The method of claim1, wherein the plurality of sacrificial fin structures are formed usinghardmask and a subtractive method applied to a material layer of saidfirst semiconductor material.
 3. The method of claim 2, wherein theisolation regions are formed between adjacent sacrificial fin structuresand are composed of silicon oxide treated with an anneal to increasedensity.
 4. The method of claim 1, wherein the first semiconductormaterial is silicon and the second semiconductor material is silicongermanium.
 5. The method of claim 1, wherein forming the secondsemiconductor material comprises an epitaxial growth process.
 6. Themethod of claim 1, wherein etching the second semiconductor materialcomprises an anisotropic etch process.
 7. The method of claim 1, whereinforming the functional gate structure comprises: thinning the hardmask;forming a gate sidewall spacer on sidewalls of a gate opening atop aremaining portion of the hardmask; isotropically etching the remainingportion of the hardmask to form an undercut region underlying the gatesidewall spacer; forming a high-k gate dielectric on sidewalls of thegate sidewall spacer and filling the undercut region; and forming a gateconductor on the high-k gate dielectric.
 8. A method of a forming aplurality of semiconductor fin structures comprising: forming asacrificial gate structure on a hardmask overlying a channel regionportion of the plurality of sacrificial fin structures of a firstsemiconductor material; forming source and drain regions on opposingsides of the channel region portion of the plurality of sacrificial finstructures; removing the sacrificial gate structure and the sacrificialfin structures selectively to the hardmask; forming a secondsemiconductor material in an opening provided by removing thesacrificial gate structure and the sacrificial fin structures; etchingthe second semiconductor material selectively to the hardmask to providea plurality of second semiconductor material fin structures; formingisolation regions between adjacent second semiconductor material finstructures of said plurality of second semiconductor material finstructures; and forming a functional gate structure on a channel regionportion of the plurality of second semiconductor material finstructures.
 9. The method of claim 8, wherein the plurality ofsacrificial fin structures are formed using hardmask and a subtractivemethod applied to a material layer of said first semiconductor material.10. The method of claim 8, wherein the first semiconductor material issilicon and the second semiconductor material is silicon germanium. 11.The method of claim 8, wherein forming the second semiconductor materialcomprises an epitaxial growth process.
 12. The method of claim 8,wherein etching the second semiconductor material comprises ananisotropic etch process.
 13. The method of claim 8, wherein forming thefunctional gate structure comprises: thinning the hardmask; forming alow-k gate sidewall spacer on sidewalls of a gate opening atop aremaining portion of the hardmask; isotropically etching the remainingportion of the hardmask to form an undercut region underlying the low-kgate sidewall spacer; forming a high-k gate dielectric on sidewalls ofthe low-k gate sidewall spacer and filling the undercut region; andforming a gate conductor on the high-k gate dielectric.